1. Field of the Invention
This invention relates to a catheter or probe with a sensor for placement within a human or animal to allow direct monitoring within the body, and more particularly, relates to a support between the sensor and an end of the catheter and a method of assembling the sensor to the support and the catheter or probe.
2. Background Art
Catheters have been inserted into humans and animals for diagnosis, monitoring and treatment purposes and such catheters have to be small and flexible in size and structure in order to function without irritating the body part into which they are placed. Typically, catheters are used to infuse medications or remove samples for purposes of analysis. Multilumen catheters are sometimes used to infuse medication and remove samples at the same time.
If a sample is removed for purposes of analysis, it has to be taken to a laboratory, analysis made and the results transmitted to the doctor. Delay in performing the analysis and transmitting the data sometimes can be fatal to the patient. Another use of a catheter is to form a hydraulic column for transmitting pressure readings to an external sensor. In connection with pressure sensors, the hydraulic column has problems of air bubbles, kinks in the tubing of the column and blood clots each of which tends to affect the reliability, waveform fidelity and the accuracy and precision of the readings.
Ideally, the catheter should be about 20 gauge in size to provide an instrument for therapy or diagnosis which is easily inserted and easy to use without irritation or injury to the body. Twenty gauge catheters are commonly used on all but pediatric patients without problems of introduction or irritation when using such catheters, particularly, in connection with peripheral vessels. A pressure sensor on the distal tip of a 20 gauge catheter or probe would eliminate the mentioned hydraulic column difficulties.
Catheter tip pressure sensors have heretofore been relatively large in size, complicated in design, and costly to manufacture and use; therefore, such catheters have not been disposable. For preventing spread of disease and infection an inexpensive and reliable single use catheter tip pressure sensor is desired. The design for a sensor support and the method of using that support to aid in assembly is also needed.
Catheters having sensors are known and include sensors mounted at the distal tip of the catheter. U.S. Pat. No. 3,710,781 shows a catheter tip pressure sensor wherein a pair of elongate pressure sensor elements are mounted on opposite sides of a support. This is done to permit as large a sensor area as practical for purposes of providing accurate reproductions of blood pressure wave forms. U.S. Pat. No. 3,480,083 shows an apparatus for measuring esophageal motility, i.e., the squeezing pressure of the esophagus. The catheter in this patent has pressure sensitive sensors spaced lengthwise along and resiliently mounted on the catheter tube for measuring variations in pressure while in or passing through the esophagus. The sensors are formed of miniaturized discrete electronic components connected to a pressure responsive diaphragm and are supported within the tube by cylindrical holders fit within the tube for holding the diaphragm at the exterior surface on the side of the tube.
U.S. Pat. No. 3,545,275 shows a device responsive to impedance used for measuring pressure with a miniaturized sensor. The sensor is responsive to diaphragm fluctuations where the diaphragm is mounted in the distal end of a small diameter tube. A small probe is disclosed in U.S. Pat. No. 3,811,427 wherein a pair of electrodes are mounted in a liquid filled chamber and are sensitive to fluctuations in a diaphragm mounted at the distal end of a catheter tube. The probe is said to be smaller than one millimeter. Two embodiments are shown. Each has a diaphragm in the distal end of the catheter and a longitudinal separator which carries the pressure responsive means and isolates the liquid from the remainder of the catheter such that fluctuations in the diaphragm are transmitted to the separator which is generally longitudinally disposed.
U.S. Pat. No. 3,748,623 discloses a sensor support which is held to the catheter tube by an outer sleeve extending distally from the end of the catheter. A shelf-like member designed to flex in response to pressure loads is the distal part of the upper portion of the sleeve. Beneath this shelf is mounted the pressure sensor. U.S. Pat. No. 4,274,423 discloses a pressure sensor mounted in the end of a needle tube exposed to a pressure-receiving hole on the side of the needle tube a pre-determined distance from the end of the needle. A support member is provided with a through-hole permitting ambient air pressure on the side opposite to the pressure receiving hole in the needle. The pressure sensor is disposed on the support member and is provided with a diaphragm with strain gauges. The diaphragm is located between the through hole and the support member and the pressure receiving hole in the needle. A protective filler material having resiliently elastic and insulating characteristics covers the surface of the pressure sensitive diaphragm and faces the side hole.
U.S. Pat. No. 4,722,348 shows a semiconductor mounted within a tubular housing in the end of the catheter tube and having a pressure inlet. Sealant protects the semiconductor which is held to the support by the double face adhesive tape which also carries the electrical conductors. U.S. Pat. No. 4,809,704 discloses catheters with the sensor mounted in the tip of the catheter supported on a base by a potting resin carried within the catheter tube. The resin is a urethane or silicone material about the sensor with appropriate openings for sampling. Assembly of the sensors within the catheters has been slow and labor intensive.